Lecture notes B65.docx

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University of Toronto Scarborough
Zachariah Campbell

Lecture 78 Sensory SystemsGeneral Principles of Sensory Function o Sensory receptorsspecialized cells that transduce sensory energy into neural activityo Receptors are energy filtersrespond to a narrow band of energyo Transduction of energyVisionlightchemical energy in the photorecptorsAuditionair pressure wavesmechanical energy which activated the auditory receptor cellsSomatosensorymechanical energy activated mechanoreceptorsTaste and olfactionchemical molecules in air and foodreceptorsPaintissue damage releases a chemical that acts like a neurotransmitter to activate pain fibersReceptive Fields Locate Sensory Events o Receptive fieldsSpecial parts of the world to which a sensory receptor respondsProvides a unique view of the world for each sensory systemHelps locate sensory events in spaceReceptors Identify Change and Constancyo Rapidly adapting receptorsDetect when something is thereEasily activated and stop responding quicklyo Slowly adapting receptorsAdapt more slowly to stimulation Receptors Distinguish Self From Other o Exteroceptivereceptors respond to external stimulio Interoceptivereceptors that respond to internal stimulihelp interpret meaning of external stimulio Optic flowstimulus configuration of visual information when we runo Auditory flowchanges in intensity of a sound because of our changing locationNeural Relays o Receptors connect to the cortex through a sequence of 4 intervening neuronso Allow sensory systems to interacto Relays allow sensory system to produce relevant actionsIe Pain receptors in the spinal cord trigger reflex that produce withdrawal movement pain pathways in the periaqueductal gray matter PAG trigger behavioral activation and emotional responses o Message modification takes place at relays Gatinginhibition of sensory info can be produced by descending signals from the cortex o Relays allow sensory interactions Sensory information gets modified by competing signals from the other sensesie McGurke Effecthearing number but the visual information is not the same as the auditory and the auditory information winsperson says what they saw on the screen instead of what they heard Central Organization of Sensory Systems o After transduction sensory information is encoded by action potentials o Presence of a stimulus encoded by increase or decrease in the discharge rate of neurono The amount of increase can encode stimulus intensityo Qualitative changes encoded by activity in different neurons o How do we perceive touch as different Sensations produced in distinct cortical regionsLearn through experienceEach sensory system has distinct wiring o Synthesiamixing of sensesEach sensory system is composed of Subsystems o Subsystemsperform distinct and special rolesex VisionReceptor Density Determined Sensitivityo Higher density of sensory receptors leads to increased sensitivity o Twopoint sensitivityability to recognize the presence of two pencil points close together o Foveaincreased density of cone cells increased ability ti ake sensitive colour discrimination in bright lighto Peripheral retinaincreased density of rod cells increased sensitivity for light Sensory Systems Have Multiple Representations o Topographic organizationneural spatial representation of the body or areas of the sensory world o Sensory systems have one primal cortical area o Additional areas secondary areas that perform specific aspects of the sensory modality Vision o Photoreceptorslocated in the retina o Two typesRodssensitive to dim light night visionlocated in peripheral retinaConessensitive to bright light day vision and colour visiondensely packed in fovea o Bipolar cellssynapse with the rods and conessend information to the ganglion cellso Ganglion cellssend axons to the brain properaxons form the optic nerveVisual Pathwayso Geniculostriate pathwayOptic nerves leave the eye and cross at the optic chiasmRight half of each eyes visual fieldleft hemisphereLeft half of each eyes visual fieldright hemisphereNext pathway relays through the lateral geniculate nucleus LGN of the thalamus LGN projects to the primary visual cortex or striate cortex or V1
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